The broad concept of a mechanical device to allow positive verification, by feel and by vision, of the presence of a cartridge in the chamber of a locked firearm is not new. Previous devices, however, have involved an undesirable compromise to the strength or the reliability of the firearm. Most have utilized a separate plunger-type probe, positioned either parallel to or normal to the centerline of the chamber. In either case, this probe has constituted an additional penetration weakening the system which supports the cartridge case, adding to those already necessitated by the feed, extraction, and ejection functions of the breech mechanism. A few approaches have involved the extractor, an already existing component, but in so doing have complicated its construction to a degree which undermines its efficiency, reliability, and cost of manufacture.
The present invention provides a direct, reliable, and inexpensive mechanical means to indicate the status of the chamber of a locked firearm, a means which does not require an additional probe to penetrate the walls of the firearm which support the cartridge case against expansion and failure from firing pressure, and does not impair the function of an existing component.
The spring-plunger type of ejector, originally introduced in the U.S. service arms of World War II, is now applied almost universally in modern high-power firearms due to its simplicity and its compatibility with breech systems giving maximum support and confinement to the cartridge case structure of modern high-pressure ammunition. It is the object of this invention to utilize, with minimal alteration to its design and function, this type of ejector as the probe for a chamber indicator. This use of this type of ejector as a probe does not significantly effect its construction, functioning, or reliability. During the closing and locking phase of the breech bolt into the receiver of a firearm, the plunger-type ejector is cammed back into the breech bolt body by the cartridge, normally a distance, parallel to the chamber axis, of about one-eighth of an inch. It is the object of this invention to utilize this displacement of the ejector plunger, by means of a very simple mechanical train, to actuate an indicator to protrude beyond an exterior surface of the firearm where it can be seen and felt. When the chamber is empty, the ejector plunger is not cammed back into the breech bolt, and the indicator means is caused by its return spring to lie substantially flush with an exterior surface of the firearm.
The specific embodiment described herein involves the application of this invention to the class of firearm breech mechanism well known in the art as the "bolt action". The embodiment is further shown restricted to the most common type of bolt action used for high-power cartridges, the Mauser type wherein the breech bolt is machined or fabricated into a one-piece body, without a separate, non-rotary, breech bolt head, so that all elements of the breech bolt body rotate together. This particular embodiment has been chosen to illustrate the invention because it represents by far the most difficult type of firearm breech mechanism to which the invention can be adapted, since the breech bolt, which houses the ejector, performs rotary, helical, and longitudinal movement relative to the receiver, which can house the indicator, during each complete operational sequence of this type of firearm.